1. Field of the Invention
This invention relates to a magnetic recording disk cartridge, and more particularly to a magnetic recording disk cartridge for a magnetic recording disk which is small in diameter and extremely thin in thickness and which is rotated at a high speed for recording or reproduction.
2. Description of the Prior Art
There has come into wide use as a recording medium for computers a floppy disk which is a flexible disk of polyester resin coated with magnetic material on both sides thereof and on which digital information is recorded by a magnetic head. The floppy disk is easy to handle and inexpensive.
Recently, there has been proposed a photographic still camera in which, instead of a conventional silver salt photographic film which cannot be reused, a magnetic recording disk smaller than the floppy disk both in thickness and diameter is used as a recording medium. This still camera is generally referred to as "an electronic camera". This electronic camera is generally about the size of a typical 35 mm photographic camera. In the electronic camera the image of an object is magnetically recorded on the magnetic recording disk while the disk is rotated at a high speed. Generally the magnetic recording disk for the electronic camera is accommodated in a hard casing to form a cartridge and is loaded in the camera body together with the casing.
The magnetic recording disk for the electronic camera comprises a recording medium which is small in diameter and is extremely thin, and a hub fixed to the center of the recording medium. The casing for the disk has a hub opening through which the hub is exposed and a pair of magnetic head receiving openings in the front and rear side walls thereof, the magnetic head receiving openings being for giving the magnetic head of the recording-reproducing system access to the recording medium. In this specification, the term "recording-reproducing system" should be broadly interpreted to include systems for recording only and for reproduction only.
In recording images using a magnetic recording medium, signals are densely recorded on the magnetic recording medium since video signals have a wider frequency band than digital signals or audio signals. Accordingly, when fine unevenness, scratches at flaking exists in the magnetic coating on the magnetic recording medium or when dust is deposited on the magnetic coating, so-called drop-out occurs during reproduction and the recorded signals cannot be faithfully reproduced. Since the magnetic recording disk cartridge for the electronic camera is frequently used outside, dust is apt to get into the inside of the casing through the magnetic head receiving openings to adhere to the surface of the recording medium and there is a danger that the part of the recording medium exposed through the magnetic head receiving openings may be brought into contact with something outside the casing to be scratched thereby, while the cartridge is being carried.
Therefore, such cartridges are generally provided with a shutter mechanism which normally closes the magnetic head receiving opening and opens when the cartridge is loaded in the recording-reproducing system. Typically, the shutter mechanism includes a pair of shutter members which are disposed on opposite sides of the recording disk. Each shutter member comprises an annular bearing portion which is engaged for rotation with an annular engaging portion formed on the inner surface of the casing at its center, and a shutter portion which radially outwardly extends from the bearing portion and is adapted to close the magnetic head receiving opening. The shutter members are fixedly fit into engaging recesses formed on one end of a strip-like connecting member the other end of which is exposed outside the casing. The shutter members are normally held, by urging means, in an operative position in which the shutter portions close the respective magnetic head receiving openings and are rotated on the respective bearing portions to an inoperative position in which the shutter portions are retracted from the respective magnetic head receiving openings to open the same when the cartridge is loaded in the recording-reproducing system and said other end of the connecting member is pushed by an abutment portion provided in the system.
However, the conventional shutter mechanism is disadvantageous in that troublesome steps are required to incorporate the shutter members into the cartridge. For example, the shutter members must be engaged with the connecting member. Further, provision must be made for preventing each shutter member from disengaging from the engaging rib to fall toward the magnetic recording disk. Typically, a plurality of projections are formed on the periphery of each engaging rib and a like number of notches are formed on the bearing portion of each shutter member. When assembling the cartridge, each shutter member is moved to receive therein the engaging rib with the notches being aligned with the projections on the engaging rib and then rotated by an angle to move the notches out of alignment with the projections after the notches clear the projections.